Part 2 of 2

Code Chart 23:

IAT Sensor Circuit:

CIRCUIT DESCRIPTION:
The Intake Air Temperature (IAT) sensor, located in the air cleaner assembly, uses a thermistor to control the signal voltage to the Engine Control Module (ECM). The ECM applies a reference voltage (4 to 5.5 volts) on CKT 472 to the sensor. When intake air is cold, the sensor (thermistor) resistance is high. Therefore, the ECM will sense a high signal voltage. As the air warms, the sensor resistance becomes less and the voltage drops.

TEST DESCRIPTION: Number(s) below refer to circled number(s) on the diagnostic chart.

1. This step determines if DTC 23 is the result of a hard failure or an intermittent condition.

2. If the ECM recognizes the open circuit (high voltage) and displays a low temperature, the ECM and wiring are OK.

Diagnostic Aids:
If the engine has been allowed to cool to an ambient temperature (overnight), engine coolant and intake air temperatures may be checked with a scan tool and should read close to each other.

^ If DTC 23 is intermittent or a "Hard Start" symptom is present, check intake air temperature with a scan tool on a cool engine. Temperature displayed should be within 5 degrees of the ambient. If not, check the IAT sensor using the "Diagnostic Aids" on the next part.